1. Field of the Invention
The invention relates to a vibration generator for seismic application comprising a housing, in which coils, activated with AC current or electric pulses, are accommodated and which is coupled via a coupling element to the investigation object.
2. Description of the Related Art
In raw material exploration seismic vibration methods for the geophysical exploring of deep subsoil structures and material properties are employed. For this purpose longitudinal and transverse waves are applied. The essential advantages of the method are the controllable signal, the high-grade reproducibility, the exact determination of the signal delay time and the damage and environtal endangerment which are low in comparison to pulse sources (for example explosives).
The same methodology is also suitable for exploring near-surface subsoil of up to a few hundred meters depth for geophysical engineering tasks. However, as a rule, the equipment utilized in the exploration for seismic excitation is too large for near-surface applications, too heavy and technically too elaborate, due to the customarily used servohydraulic driving technology to be able to employ it at justifiable costs on a considerably size-reduced scale.
For near-surface tasks with vibration processes, electric driving systems are better suited, since they require considerably less technical expenditures. Vibration generators driven in this way are successfully employed for example in stationary material testing. In these systems, moving coil systems (deflection of a coil in a toroidal core magnet) similar to a dynamic loudspeaker are utilized for converting electrical into mechanical energy. Technically problematic is the precise friction-less guidance of the moving coil in the toroidal core in the presence of radial forces. Furthermore, powerful permanent toroidal magnets necessitate a large weight.